<!DOCTYPE html>
<html>

<head>
  <title> new document </title>
  <meta charset="utf-8">
  <script src="js/jquery-1.11.3.js"></script>
  <style>
    .alert {
      border: 1px solid #a33;
      color: #922;
      background: #fee;
      padding: 10px;
    }

    .alert>.close {
      float: right;
      font-weight: bold;
      opacity: .5;
      cursor: pointer;
    }

    .alert>.close:hover {
      opacity: 1
    }

    /*定义淡入淡出动画的初始状态,常驻元素*/
    /* .fade {

      } */
    /*定义淡入淡出动画的结束状态*/
    /* .in {

      } */
  </style>
</head>

<body>
  <button id="btn">click me!</button>
  <div class="alert fade">
    <span class="close">×</span>
    <p>您的浏览器版本太低!请下载最新版本的浏览器</p>
  </div>
  <script>

  </script>
</body>

</html>